Samples of lots subject to the rabbit pyrogen test submitted to the Center for Biologics Evaluation and Research for release are first testing using the LAL test. All samples with a positive lysate test at a dilution of 1:32 or greater are then tested using the standard rabbit pyrogen test (Title CFR 600.13(b) (1), (2), (3)). In addition, lots are selected in the usual fashion for the rabbit pyrogen test. With only few exceptions, there has been a positive correlation between the rabbit pyrogen test and the LAL test. This study will provide the basis for use of the LAL test instead of the rabbit pyrogen test in the quality control of products where appropriate. The study will be continued in order to gather further data comparing the LAL and rabbit pyrogen test in a wide variety of biological products.